whenever you place a trade in the market there is a risk that it will not work, hence the reason for a stop loss to restrict your losses to allow you to trade at another time. However your set-up should provide you with a higher balance of probability that it does work in your favour.
With this in mind when you approach the trading day in order to follow your trading system properly there will come a time when you either get stopped out or your mental stop is reached and you close for a loss. If you have followed your trading plan then you could consider it that you have not a loss in the usual sense but took a businessman's risk. It is the risk you have given up which you were prepared at the start of your deal to accept.
Following on then you might consider a loss as more than that which you were originally prepared to risk and not keeping to your stops. If you get stopped out to frequently one day then maybe it is a day to miss or your system is not quite complete or you have just followed your trading plan to the letter and your risks have not worked out today. But there is always tomorrow.